Epidemiologic study of viral respiratory infection in children and comparison between the direct and indirect immunofluorescent assay

Chun, Lae Hee; Kang, Jung Oak; Minn, Doh Sik; Park, Ile Kyu; Oh, Jae Won; Choi, Tae Yeal

Abstract

BACKGROUND
Studies on the incidence and seasonality of respiratory viruses that are the main cause of lower respiratory tract disease in children are insufficient in Korea. In the present study, the epidemiology of respiratory viruses in children was studied during the last 2 years and, the indirect immunofluorescent (IF) method was compared with the direct IF method.
METHODS
A total of 814 pediatric inpatients hospitalized for lower respiratory tract infection at Hanyang University Hospital were studied from April, 1996 to July, 1998. Nasopharyngeal aspirates were obtained from these patients and indirect IF (Respiratory Panel I Viral Screening & Identification Kit, Light Diagnostics, Chemicon, Temecula, CA, USA) was performed for the following viruses : respiratory syncytial virus (RSV), parainfluenza virus type I, II and III, influenza virus A, B, and adenovirus. Sixty-nine of these samples were tested by direct IF (IMAGENTM, DAKO, UK) and indirect IF, simultaneously.
RESULTS
1) Viral pathogens were detected in 30.5% of nasopharyngeal aspirates. Among the positive cases, RSV was 60.6%, influenza A 35.3%, adenovirus 5.2%, influenza B 4.0%, and parainfluenza II 0.8%. 2) The occurrence rate of RSV in spring, summer, fall and winter was 7.3%, 13.6%, 31.45%, 33.45%, respectively, and showed a unique pattern in that the incidence rate in the summer of 1997 was 22.2%. A unique pattern was also observed for influenza A, which was continuously detected from December 1997 to July 1998. 3) The positive rate of indirect IF was statistically higher than that of direct IF. Excluding the results of the influenza A, there was no statistically significant difference between the two methods.
CONCLUSION
RSV was the most frequently detected virus in viral respiratory infections in children. Infection usually began in the fall and most frequently detected in the winter and lasted until spring. High incidence of RSV in summer 1997 and continuous detection of influenza A till summer 1997 suggest some change of epidemic pattern. The discordance between direct and indirect IF was probably due to the difference in quality of the anti-influenza A reagent rather than a real difference in the two methods.